Page 583 - Polymer-based Nanocomposites for Energy and Environmental Applications

536 Polymer-based Nanocomposites for Energy and Environmental Applications

potential μ A with respect to that of the cathode one (μ C ) to provide a high-cell voltage,
+
(iii) optimized Li ion accommodation to provide high capacity, (iv) and chemical
stability with respect to the used electrolyte.
Carbon-based ones, especially graphite, are currently used as anode materials in
commercial devices because they are abundant and cheap and have good performance.
However, many other materials have interesting physical characteristics and advan-
tages over carbonaceous ones. First, metal Li would be the best for use as anode mate-
rial because of its low negative redox potential ( 3.040 V) and a high-specific
capacity ( 3860 mAh/g) obtained in the cells [126]. However, Li anode meets two
major drawbacks: (i) a possible reaction with the electrolyte and (ii) a risk of electric
short due to the growth of Li dendrites. These problems impact on the safety of battery
use and hence on their commercialization. It has also been proposed to utilize nano-
structured materials for anodes in LIBs in order to address the strain development
problem. Indeed, by their small size, these materials can limit the maximum concen-
tration of lithium and thus reduce the strain in the layer. In a nanoporous structure, the
stress can be also reduced since the pores play the role of a buffer and attenuate the
volume change of the layer.
Conjugated polymers have been investigated for use as cathode materials in LIBs
because of their relatively good electric conductivity. At the anode, polymers have
been initially investigated as a binder (matrix to hold inorganic nanoparticles),
namely, with silicon to address the volume variation issue due to lithiation processes.
As they have also good electric properties, composites made of conjugated polymer
and anode materials have been realized and used for improving both mechanical and
electrochemical performance of batteries. For instance, PPy polymerized onto graph-
ite powder and used as an anode could significantly improve the cell capacity by
reducing its resistance as compared with bare graphite anode cell [127]. PPy has been
also used with Si nanopowder, carbon black, and PVDF to form anode material in
LIBs [128]. The cells showed high-coulombic efficiency at high-cycle life, which
is assigned to the improved mechanical and electric properties of the anode material.
The use of GO coated with phenol formaldehyde resin as anode has been proved to
reduce strongly the SEI film and improve significantly the cycling stability and the ion
storage capacity of the cells [129]. Other polymer-based composites utilize PEDOT,
which is a highly conductive polymer and currently used as a material for buffer layer
in organic electronic devices. Composite films made of PEDOT and porous nickel
oxide have been formed by electrodeposition technique and used as an anode in LIBs
[130]. The battery exhibited high-cycling performance and high capacity, which are
assigned to the large contact polymer/oxide surface and the high-electric conductivity
of the polymer.

Electrolytes
In a battery, the electrolyte transports ions from one electrode to the other. It plays an
essential role in the stability and the current density because it interacts directly with
the electrode and the separator. The formation of the SEI between an electrolyte and
the electrodes strongly affects the chemical stability of the latter and impacts on the